A remote power controller (RPC) is a form of switching circuitry that offers remote switching of a high power electrical load from its source with a low power control signal bus. RPCs are particularly useful in aerospace applications to reduce weight, bulk, cost and power loss associated with high power remote power switching, which type of switching requires advanced features including an overload trip function, status outputs, and, often, current limiting.
Current limiting provides control of excessive currents in electrical systems when the outputs experience a fault condition. RPCs limit load current by controlling the load current to some value in excess of normal value whilst sustaining the electrical potential difference between the power source and the load. A short in the load circuit maximises power dissipation in the RPC, since the full electrical potential difference of the power source voltage then exists across the RPC.
Since RPCs have semiconductor-based current limiting devices, these devices must dissipate significant amounts of power. Since some applications may require the dissipation of hundreds of watts, RPCs may require tens of semiconductor-based current limiting devices to operate in parallel to achieve such power dissipation. Certain RPC designs have used so-called “helper” circuits that divert some of the load current to a resistor under fault conditions, reducing power dissipation for the semiconductor-based current limiting devices. Under ideal conditions, the “helper” circuit can reduce the power in the semiconductor-based current limiting devices by 75 percent. With practical tolerances, the power reduction is less than 60 percent at best.